Considerations for Small Grain Weed Control

Mark VanGessel, Extension Weed Specialist;

If planting as no-till or minimum tillage, be sure to “start clean” with a burndown herbicide. A turbo-till is not a tillage implement for weed control, so often these fields need a burndown herbicide, particularly if the field is infested with annual bluegrass. Poor weed control is often due to the weeds being too large and that can be traced back to not starting clean.

There has been an interest in using herbicides at planting (or shortly after planting) for weed control. There are few effective herbicides labeled for preemergence applications. Sharpen is labeled for wheat and barley but provides limited control. Valor or Afforia can be used with the burndown application, but there must be a minimum of 7 days between application and planting wheat. We have seen injury with Afforia or Valor used on coarse-textured soils, practically if rain occurs shortly after planting or if seed is planted less than 1 inch deep.

Finesse CF (cereal and fallow) can be used preplant or preemergence with wheat; it can tankmixed with glyphosate or paraquat to provide residual control of a henbit and common chickweed. Be aware that Finesse will not control ALS-R common chickweed. Rotational restrictions limit planting only Bolt or STS soybeans after harvest; sorghum rotation is 4 to 18 months depending on rate, and field corn and non-STS soybeans is 18 months.

Peak can also be applied prior to planting wheat and barley. Rotation to field corn and sorghum is 1 month, and 10 months to soybeans (STS and non-STS). Peak has provided good henbit control in limited UD trials, but will not control ALS-resistant chickweed.

Axiom, Anthem Flex and Zidua can be used after wheat emergence, typically at the spike stage. These products are only labeled for winter wheat, not barley. They do not provide control of emerged weeds, but can have utility in situations where application can be made after wheat emergence but before weed emergence. These three herbicides require rainfall or irrigation to activate, so if we experience a dry spell after application, control can be compromised.

Axiom, Anthem Flex, Zidua, Finesse, Valor and Afforia all specify that the seed must be planted at least 1 inch deep. None of these products are compatible with wheat planted by “spinning the seeds” on the soil surface and shallow incorporation with a disk or turbo-till.

As far as postemergence treatments, fall herbicide applications have been more consistent and achieved overall better weed control than spring treatments in our trials. This is an important consideration for small grains planted in the early fall. The soil temperature remains warm for weeks after the first frost and this keeps the weeds in an active state. I find annual bluegrass, henbit, or speedwells species are often more susceptible if treated in the fall compared to early spring. Once we have consistently cold weather and soil temperatures drop, then fall treatments will be questionable. Fields may need a spring herbicide application for wild garlic control, but often broadleaf weed control is excellent with fall treatments.